@Knallfrosch Use another LAN port on the FritzBox side, where the problematic Archer C6 is connected. If the issue persists change the ethernet cable of the problematic Archer C6 with a prooved good...

Here comes the DDNS feature in the Synology DSM or in your router.

@Capricorn12 1) From my router to the Bix box (junction box) I have and old Category 5 cable (20 feet long) which I believe is limited to 100 mbps, and from the Bix box to the UniFi AC AP Pro, it's a...

@Madman1939 Go through this thread to see how can you troubleshoot this issue.

@BugoK The FW upgrade is not likely to be the reason for your issue. Unplug all LAN connected devices, reboot the router and start plugging them one-by-one to check if any of these causing an issue....

@Capricorn12 Happy holidays ! 1) Can I use the ax6000 as my primary router and connect the Unifi AP Pro to get greater wi-fi coverage and signal strength in the basement and the garage? Yes. 2) If...